(1) An improved purification pocedure using the HPLC technique has been developed to purify the Mg(II)-ATP-dependent protein kinase from rabbit skeletal muscle. The purified enzyme consists of 38 and 31 KDa subunits, which correspond to the catalytic and modulator subunit, respectively. A mechanism for the activation of the inactive enzyme involves a transient phosphorylation of the modulator subunit catalyzed by kinase Fa. A few lines of evidence in support of the phosphorylation induces the catalytic subunit to its active form includes the observation that removal of the modulator by limiting proteolysis fails to activate the inactive (native) enzyme, unless it has been first phosphorylated or thiophosphorylated. Evidence supporting the slow isomerization which leads the active enzyme to its inactive form was demonstrated. The regulatory subunit (R) of type II cAMP-dependent protein kinase is an effective inhibitor for the phosphatase. A curve fitting method was used to estimate the dissociation constants for R.phosphatase, R.type I catalytic fragment and Fa.phosphatase complexes. The results suggest that R binds to the catalytic subunit. In addition, computer simulation of a cyclic cascade using the cAMP-dependent protein kinase and the above phosphatase as converter enzymes revealed that they constitute a highly efficient regulatory machanism. (2) A comparative study of cyclic cascade and simple allosteric control revealed that simple allosteric control cannot provide the same regulatory efficiency as those exhibited by the cyclic cascade systems. (3) A simple treatment was developed to describe interfacial reaction dynamics. This analysis revealed those conditions under which reduced dimensionality can be expected to enhance the overall efficiency or reaction rate of a bimolecular reaction. (4) A study of skeletal muscle actomyosin ATPase cycle using subfragment-1 in place of myosin revealed that a six-state model, which consists of six myosin bound reaction intermediates containing phosphate in the form of ATP or ADP.Pi, is the simplest kinetic model required to describe the ATase cycle.